The US banks are already exposed to the risk of European banks. As the Euro banks continue to fail in a true domino effect, the US banks will share in those losses. When the US banks take big losses and begin to fold themselves then the federal reserve will bail the US banks out. As we have already seen, they are considered to be "to big to fail". The Fed will do this by creating money out of thin air and they don't need permission from Obama or anyone else to do it.